Yellowjackets are stinging insects that build large communal hives. Three kinds of yellowjackets occur in San Mateo County: the Western Yellowjacket (Vespula pensylvanica), Common Yellowjacket (Vespula alascensis) and the Aerial Yellowjacket (Dolichovespula arenaria). The first two build hives under the ground and feed on live insects, dead animals, and nectar. These are the insects that pester you during your summer and fall BBQs. Aerial yellowjackets build large paper nests in trees or other high places (such as the eaves of your house).

Paper wasps are similar to muddaubers. Females are solitary and build small nests from paper. These nests often appear along the eaves of homes during summer months. They are papery, two to four inches across, and have a honeycomb appearance when viewed from below.

Muddaubers belong to the family Sphecidae. They have a very thin waist and long, dangly legs. These wasps are incredibly beautiful, with smoky wings and a bright metallic blue body. There are more than 1,100 species in this family in North America. All are solitary with each female building an individual nest in which to lay her eggs. The nests are made out of mud, two to three inches across, with rows of round cells containing the developing embryos. The female wasp stocks each cell with a spider—food for the young wasps when they hatch.